1. Field
Embodiments relate to a power supply device and an image forming apparatus having the power supply device, and more specifically, to a power supply device configured to limit auto-restarting of pulse width modulation (PWM) IC and an image forming apparatus including the same.
2. Description of the Related Art
An image forming apparatus operates to generate print data, and perform printing, receiving and transmitting such image data. Representative examples may be printers, scanners, copy machines, fax machines or multi-functioned units combining the foregoing functions therein.
The image forming apparatus is provided with electrical power by using internal switched-mode power supply (SMPS). SMPS includes a PWM IC which provides a protection function against external situations through circuit constitutions. PWM IC includes protection functions such as OCP (over current protection), OLP (over load protection), OVP (over voltage protection), or TSD (thermal shot down protection), and PWM IC performs controlling load characteristics on secondary circuits by performing the feedback controlling.
When protection functions are performed as described above, PWM IC performs auto-restart function. However, regarding loss on the secondary circuits as well as temporary increases of loading, voltage and current, when PWM IC is auto-restarted with the protection operation, peak voltages may occur in FFT, second output diode and second output voltage due to delivered energy at the time point of switching for the auto-restart. Thus, there may be a problem that secondary bad operating occurs. The problem will be explained by referring to FIGS. 9A and 9B.
FIGS. 9A and 9B illustrate output waveforms in the related PWM IC when transient situation occurs. FIG. 9A illustrates PWM switching waveforms in transient situation and FIG. 9B illustrates waveforms of output voltage on the secondary circuits in transient situation.
Referring to FIGS. 9A and 9B, when preset time elapses since the PWM signal output is stopped in response to transient situation as sensed, the PWM IC automatically performs the auto-restart. Thereby, peak voltage of output voltage is generated at the primary and secondary circuits.
When output voltage on the secondary circuits exceeds a preset voltage, PWM IC senses this and accordingly stops PWM operation. When output voltage on the secondary circuits is stabilized, PWM IC performs PWM operation again with the auto-restart. At this process, the second diode, i.e., an output end may generate peak voltage. As the auto-restart is repeatedly performed, the components of the secondary circuits are subject to stress. Further, when peak voltage is repeatedly outputted, components connected to the secondary circuits may be damaged.